A V-8 engine has two engine heads and eight valve spring assemblies per head. The valve spring assemblies comprise a valve, spring, spring retainer and two half rings called keys. To insert the valve spring assemblies into the engine head, the spring must be compressed so that the keys can be placed around the valve stem notch. When the spring is released, the keys are firmly held in place. If one key should pop out as the spring is released, the other key will temporarily hold the assembly together. Because of human errors, the manual inspection operation performed after engine head assembly is less than perfect, and some percentage of the assembled engines do not contain both keys on each of the potentially eight valve spring assemblies of an engine head. Missing valve retainer keys can cause production delays and increase cost if they are discovered late in the assembly stage or during the engine testing phase. If they are not detected at all, the missing keys can lead to serious engine damage in the field.